$_POST returning null on server, but works fine on mamp localhost – Apache

Hello everyone,

I’m a Newbie web app developer. Recently, I finished my project on Mamp
and trying to move everything into server. Then odd things happened. The $_POST
function all of sudden does not work.

I googled this question for two days and tried many things. Like
changing apache config, reinstall some php package. I tried to use .htaccess, but did not figure out how it works. I just wondering is there
any other way to make this thing works as i tested on mamp.

By the way,i use LAMP in server.

Here is php code. var_dump($_POST) will return null and
var_dump($_REQUEST) will return array{}.

   $conn = new mysqli($servername, $username, $password, $dbname);
 // Check connection
 if ($conn->connect_error) {
  die("Connection failed: " . $conn->connect_error);
 } 
  $ID=$_POST['Client_ID'];
  $name=$_POST['username'];
  var_dump($_POST);
  $sex=$_POST['sex'];
  $mobile=$_POST['mobile'];
  $email=$_POST['email'];
  $time=$_POST['time'];
  $company_name=$_POST['Company_name'];
  $wechat_id=$_POST['Wechat_id'];

  if ($sex==0){
    $sex="female";
  } else {
   $sex="male";
  }
  $delOrnot=0;




  $sql="INSERT INTO Client(client_id,owner_name,gender,cell_phone,email,time,company_name,delOrnot,department) VALUES ('{$ID}','{$name}','{$sex}','{$mobile}','{$email}','{$time}','{$company_name}','{$delOrnot}','{$wechat_id}')";


if($conn->multi_query($sql)===TRUE){
     echo"New records created successfully";

  }else {
    echo "Error " . $sql . "<br>"  . $conn->error;
    }
  $conn->close();

Here is html code.

<form action="member-add.php" method="post" class="form form-horizontal" id="form-member-add">
    <div class="row cl">
        <label class="form-label col-xs-4 col-sm-3"><span class="c-red">*</span>userID：</label>
        <div class="formControls col-xs-8 col-sm-9">
            <input type="text" class="input-text" value="" placeholder="" id="Client_ID" name="Client_ID">
        </div>
    </div>
    <div class="row cl">
        <label class="form-label col-xs-4 col-sm-3"><span class="c-red">*</span>username：</label>
        <div class="formControls col-xs-8 col-sm-9">
            <input type="text" class="input-text" value="" placeholder="" id="username" name="username">
        </div>
    </div>
  </form>

And it works perfectly on mamp. I don’t know what is wrong on my server configurations. Thank you for your kindly help!